As Sen. Tom Carper took aim at the president at a Democratic primary debate Monday night, his challenger, Kerri Evelyn Harris, hurled criticism at Carper.

"He voted for the Keystone pipeline," said Harris, an Air Force veteran and community advocate, amid boos at her opponent. "He voted to confirm Rick Perry who is bringing back coal plants that are polluting the air. He voted to allow Tyson chicken company to stop reporting their harmful emissions."

To Carper, she said: "All of your votes count. Not just the ones you can pat yourself on the back for."

Carper, 71, has both the advantage and vulnerability of having decades of political experience. A senator for 18 years and Delaware's governor, U.S. representative and treasurer before that, Carper said he's running to fight for healthcare and against President Donald Trump's "really stupid ideas on trade and on the economy."

Harris, who has sworn off corporate cash, lacks the $1.3 million campaign war chest Carper recently reported to federal officials. She had only $15,000 on hand as of June 30.

But she is bolstered by the energy of liberal Democrats like Alexandria Ocasio-Cortez, the 28-year-old Democratic socialist who primaried and beat 19-year incumbent Joe Crowley for his U.S. representative seat in June.

Like Ocasio-Cortez, Harris emphasized progressive talking points such as a $15 minimum wage, affordable health care as a "human right," and the wiping out of college debt.

Carper has recently advocated more for a higher minimum wage and agreed with Harris that the health care system needs improvement — but he stopped short of supporting Harris's proposal to "eliminate all student debt and start fresh."

"I don’t have a magic wand that would enable us to do that," he said. "It would cost a pretty penny."

After Carper detailed his support for federal Pell grants and loan forgiveness for graduates who pursue careers in public service, Harris fired back at the senator.

"We found a way to bail out the banks that were too big to fail," she said.

Harris told the audience of about 700 that her lack of "experience" is her strength.

"The problem is we need diversity in experience," said Harris, who criticized Carper for voting to confirm Trump's Supreme Court nominee Brett Kavanaugh to a federal appeals court in 2006.

"If everyone is viewing the world through the same lens, you get people like Kavanaugh because you spoke to people in your network and they told you he’s a good guy."

Carper said at the debate that Kavanaugh came recommended by members of the Delaware legal community back then, and he voted "on my hopes over my fears."

"I will not do that again," he said.

Harris and Carper, along with Republicans Eugene Truno and Robert Arlett, will appear on their parties' ballots during the Sept. 6 primary election. Winners from each party will face off in the November general election.

In a question and answer session, Truono expressed his commitment to "state's rights" and the idea that mass gun violence is a mental health issue. He also said he supports the Republican tax cuts and "allowing the free market system to work" when it comes to the cost of college.

On abortion, Truono said he is "pro-life" and would support banning the termination of pregnancies after 20 weeks.

"My Democratic opponents will talk about Medicare for all," he said to perhaps unintended applause in a room that appeared to be full of Democrats. "I do not support that. It’s not sustainable."

Several times on Monday, Carper touted his experience fighting the Trump administration and applauded the departure of former Environmental Protection Agency administrator Scott Pruitt.

"Good riddance," said Carper, the top Democrat on the Environment and Public Works Committee.

Asked what can be done to combat political gridlock when it comes to immigration, Carper said the best thing to do would be to "change presidents."

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. (Photo: Jerry Habraken, The News Journal-USA TODAY NETWORK)

"The second thing we could do is change majorities in the House and Senate," he said.

In the end, Harris said that Carper already had his chance to make Delaware and the country better.

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. Jerry Habraken, The News Journal-USA TODAY NETWORK

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. Jerry Habraken, The News Journal-USA TODAY NETWORK

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. Jerry Habraken, The News Journal-USA TODAY NETWORK

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. Jerry Habraken, The News Journal-USA TODAY NETWORK

The crowd reacts to an answer during a U.S. Senate debate between Sen. Tom Carper and Democratic primary candidate Kerri Evelyn Harris Monday night at Cab Calloway School of the Arts. Jerry Habraken, The News Journal-USA TODAY NETWORK